Cnidaria in UK coastal waters: description of spatio-temporal patterns and inter-annual variability - Cambridge University Press
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Journal of the Marine Biological Association of the United Kingdom, 2014, 94(7), 1401 –1408. # Marine Biological Association of the United Kingdom, 2014. This is an Open
Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted re-use,
distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/S0025315414000137
Cnidaria in UK coastal waters: description of
spatio-temporal patterns and inter-annual
variability
stephen k. pikesley1,2, brendan j. godley1, sue ranger1,3, peter b. richardson3
and matthew j. witt2
1
Centre for Ecology and Conservation, University of Exeter, Cornwall, TR10 9EZ, UK, 2Environment and Sustainability Institute,
University of Exeter, Cornwall, TR10 9EZ, UK, 3Marine Conservation Society, Ross on Wye, HR9 7QQ, UK
Concern has been expressed over future biogeographical expansion and habitat capitalization by species of the phylum
Cnidaria, as this may have negative implications on human activities and ecosystems. There is, however, a paucity of knowl-
edge and understanding of jellyfish ecology, in particular species distribution and seasonality. Recent studies in the UK have
principally focused on the Celtic, Irish and North Seas, but all in isolation. In this study we analyse data from a publicly-
driven sightings scheme across UK coastal waters (2003 –2011; 9 years), with the aim of increasing knowledge on spatial
and temporal patterns and trends. We describe inter-annual variability, seasonality and patterns of spatial distribution,
and compare these with existing historic literature. Although incidentally-collected data lack quantification of effort, we
suggest that with appropriate data management and interpretation, publicly-driven, citizen-science-based, recording
schemes can provide for large-scale (spatial and temporal) coverage that would otherwise be logistically and financially
unattainable. These schemes may also contribute to baseline data from which future changes in patterns or trends might
be identified. We further suggest that findings from such schemes may be strengthened by the inclusion of some element of
effort-corrected data collection.
Keywords: citizen science, jellyfish, life cycle, public sightings, Scyphozoa, Hydrozoa
Submitted 18 September 2013; accepted 20 January 2014; first published online 4 June 2014
INTRODUCTION (positively or negatively) abundance and distribution of
marine planktonic communities (Hays et al., 2005). These
The past decade has seen concerns expressed over blooms, factors may also be related to increases in abundance associated
future biogeographical expansion and habitat capitalization with opportunistic expansion, following decreased predatory
by pelagic species of the phylum Cnidaria (Mills, 2001; pressure as a result of declining fish abundance due to commer-
Brodeur et al., 2002; Lynam et al., 2006; Attrill et al., 2007; cial fisheries (Pauly et al., 1998; Mills, 2001; Lynam et al., 2006).
Purcell et al., 2007; Richardson et al., 2009). Gelatinous plank- Large-scale spatial knowledge and understanding of jelly-
ton (subsequently referred to as jellyfish) blooms in coastal fish ecology is data deficient (Doyle et al., 2007; Purcell,
waters can have negative implications for human activities 2009), although local scale insight has improved. For coastal
(Purcell et al., 2007; Purcell, 2009), with both social and eco- waters of the UK, an extensive review of historic literature
nomic repercussions (Doyle et al., 2007), as well as potential (100 years) (Russell, 1970) exists, and more recently, jellyfish
impacts on other species competing for the same habitat medusae studies have focused on the waters of the Celtic,
(Lynam et al., 2005a). Irish, and North Seas as well as the Solent estuarine system
Fluctuations in jellyfish abundance have potentially been on the south coast of the UK. These studies have used a
linked with climate indices such as the North Atlantic variety of methods to obtain data, including: ships of oppor-
Oscillation (NAO) and the North Pacific Decadal Oscillation tunity (Doyle et al., 2007; Bastian et al., 2011a); trawl
(NPDO) (e.g. Lynam et al., 2004, 2005b; Purcell, 2005) as surveys (primarily as by-catch; Lynam et al., 2005b, 2011;
well as variation in sea surface temperature (SST) (e.g. Lynam Bastian et al., 2011b); aerial surveys (Houghton et al., 2006a,
et al., 2011), pH (Attrill et al., 2007), salinity (Bastian et al., b; Lilley et al., 2009); electronic tagging (Hays et al., 2011);
2011a), eutrophication (Purcell et al., 2007) and habitat modi- shoreline surveys (Doyle et al., 2007); and analysis of historical
fication (Richardson et al., 2009). Future climate change may records (Lilley et al., 2009).
modify oceanographic dynamics, thereby further influencing Analyses of incidentally-collected sightings/strandings
data, from public recording schemes for other marine
species, have identified significant spatial and temporal pat-
Corresponding author:
terns and trends and provided insight into regional and
M.J. Witt large-scale national distributions (Witt et al., 2007, 2012;
Email: M.J.Witt@exeter.ac.uk Leeney et al., 2008; Pikesley et al., 2012). In the UK, a
1401
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https://doi.org/10.1017/S00253154140001371402 stephen k. pikesley et al.
public sightings scheme (http://www.mcsuk.org/sightings/ between 2004 and 2009 (N ¼ 951, 13.2% of records) from a
jellyfish.php) managed by the Marine Conservation Society single location, Harlech Bay, North Wales, (~5.5 km of coast-
(MCS), UK, allows members of the public and other interested line). As these data, in part, conformed to a pseudo-
parties to report sightings and strandings data for eight species standardized survey method they were removed to minimize
of Cnidaria. These include six species of the class Scyphozoa: bias and analysed separately. In total, 5051 records were retained
Aurelia aurita (Linnaeus, 1758) (moon); Cyanea capillata for eight species of Cnidaria. Each of these remaining records
(Linnaeus, 1758) (lion’s mane); Chrysaora hysoscella represented single or multiple sightings, beached or at sea.
(Linnaeus, 1766) (compass); Cyanea lamarckii (Péron &
Lesueur, 1810) (blue); Pelagia noctiluca (Forsskål, 1775)
(mauve stinger) and Rhizostoma octopus (Macri, 1778) (root Statistical analysis
mouth or barrel); and two species of the class Hydrozoa: To investigate any relationship between sightings by year and
Physalia physalis (Linnaeus, 1758) (Portuguese man-of-war); preceding winter NAO (December, January, February and
and Velella velella (Linnaeus, 1758) (by-the-wind-sailor). March) climate indices data were sourced (UCAR, 2013). To
The last two species are not true ‘jellyfish’ but are included contextualize the number of yearly records received in relation
in the MCS ‘Jellyfish’ Survey data for completeness, as they to public awareness of the sightings scheme, a measure of
are occasionally found in coastal waters and on beaches of yearly promotional effort (number of press hits that publicised
the UK. As far as we are aware, this database has the largest the scheme) for printed media (2003 to 2010) was categorized
spatial and temporal coverage for jellyfish sightings in UK using an ordinal scale of 1 (minimum) to 3 (maximum).
coastal waters. Spearman’s rank correlations were calculated to investigate
Here we describe spatial and temporal patterns (including any relationship within our data between sightings by year as a
seasonal and annual trends) for these eight species of the proportion of all sightings and (a) preceding winter NAO and
phylum Cnidaria, across the coastal waters of the UK, (b) promotional effort of the database. Generalized linear
between 2003 and 2011 (9 years), as recorded by the MCS modelling (GLM) was used to investigate species-specific
UK national ‘Jellyfish’ Survey database. sightings as proportion of all sightings by year. Statistical ana-
lysis was undertaken with the program R (R Development
Core Team, 2008).
MATERIALS AND METHODS To calculate the density of sightings we used a polygon
sampling grid, divided by UK regional areas, to sum the coin-
Data preparation cident length of coastline and sightings locations for each
polygon. This enabled us to calculate sightings km21 for
The MCS ‘Jellyfish’ Survey was initiated in 2003 to enhance each region. To ascertain a spatial pattern of species richness
the understanding of the spatial and temporal patterns of jelly- we used a polygon sampling grid of 50 × 50 km squares to
fish occurrence in UK coastal waters, through the recording of sum individual species occurring in each grid square. To
sightings and strandings of the adult medusae. The MCS pro- investigate the potential for spatial patterns in cnidarian
motes public awareness of this scheme annually, typically at aggregations we used the same polygon sampling grid to
the end of July, through national and regional media releases sum individual species-specific sightings of 100 Cnidaria or
(newspaper, radio and television). Awareness of the scheme is more.
also furthered by marketing via the MCS website and by dis-
tribution of promotional materials, including electronic and
hard copy ID cards (Supplementary Figure S1). Members of
the public were required to submit their written records of RESULTS
sightings and strandings by post, using a standardized form,
but this was superseded in 2007 by an on-line submission Temporal variation and species composition
form.
The MCS UK database held 7229 records (2003 – 2011). A main database
Geographical Information System (GIS) (ArcMap 10: ESRI, Sightings of jellyfish fluctuated annually, with peak years being
Redlands, US, http://www.esri.com) basemap was used for 2004, 2005 and 2009 (Figure 1A; Supplementary Figure S2).
the UK and Ireland using coordinates conforming to the There was no statistically significant correlation between
British National Grid (BNG) projection (metres). The loca- yearly sightings and promotional effort of the scheme or
tions of all sightings/strandings, hereafter referred to as sight- between yearly sightings and winter NAO. Seasonality was
ings, were converted from Ordnance Survey grid references to clearly evident, with the number of records peaking in the
decimal degree coordinates (longitude, latitude: WGS84); the months of June, July and August (Figure 1B).
year and month of occurrence for all sightings were also deter- The most commonly sighted species was Aurelia aurita
mined. These location data were added to the basemap, apply- (N ¼ 1460, 28.9% (of validated records)), there were also
ing a transformation from WGS84 to BNG. These data were regular sightings for Cyanea capillata (N ¼ 920, 18.2%),
then validated as follows. Records without location data Chrysaora hysoscella (N ¼ 955, 18.9%), Cyanea lamarckii
and/or date (N ¼ 110, 1.5% of records), without species iden- (N ¼ 756, 15%) and Rhizostoma octopus (N ¼ 483, 9.6%)
tification (N ¼ 444, 6.1% of records) were removed. Absence (Figure 1C). Of these, R. octopus was the only species with
records (no sightings recorded) (N ¼ 673, 9.3% of records) year-round presence (Figure 1D). The only other scyphozoan
were removed as there was no record of effort associated or ‘true’ jellyfish, Pelagia noctiluca was only recorded
with these data and therefore they could not provide a mean- occasionally (N ¼ 91, 1.8%), with infrequent sightings
ingful contribution to the analysis. One individual recorder (Supplementary Figure S3E). Chrysaora hysoscella sightings
was identified within the dataset who had contributed data significantly decreased during this study (GLM: F1,7 ¼ 12.39,
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https://doi.org/10.1017/S0025315414000137cnidaria in uk coastal waters 1403
Fig. 1. Sightings for all cnidarian species expressed as a percentage of sightings from 2003 to 2011 (main database): (A) by year; (B) by month; (C) species-specific
sightings expressed as a percentage of all sightings from 2003 to 2011; (D) species-specific sightings by month. Box shows median and inter-quartile ranges. Box
widths are proportional to the square-roots of the number of observations in the box, outliers are not drawn. In (A) asterisks indicate an assessment of the yearly
promotional effort of the jellyfish sightings scheme categorized using an ordinal scale of 1 (minimum) to 3 (maximum) promotional effort. In (C) and (D) species
are identified as follows: A.a., Aurelia aurita; C.c., Cyanea capillata; C.h., Chrysaora hysoscella; C.l., Cyanea lamarckii; P.n., Pelagia noctiluca; R.o., Rhizostoma
octopus; P.p., Physalia physalis; V.v., Velella velella.
P , 0.01); this was the only species for which there was a stat- the year (Figure 2D). There was a marked decrease in the pro-
istically significant trend. The Hydrozoa, Physalia physalis portion of R. octopus sightings in 2008 and 2009, 20% and 33%
(N ¼ 211, 4.2%) and Velella velella (N ¼ 175 3.5%) were of annual sightings, respectively, compared with the peak year
also recorded infrequently with P. physalis having a very for R. octopus sightings 2006, 63% of annual sightings
short sightings season (Figure 1D), with the vast majority of (Supplementary Figure S4E). There were no recorded sight-
sightings occurring in 2008 and 2009; 93% of all P. physalis ings for P. noctiluca or P. physalis (Figure 2D).
records were attributable to these years (Supplementary
Figure S3G).
Spatial distribution
harlech bay database Within the main database for UK coastal waters (excluding
Peak years for sightings of jellyfish from Harlech Bay (location the Republic of Ireland) the greatest number of sightings
map: inset Figure 2C) were 2004, 2005 and 2006; records of were from western shores (Figure 3A; Table 1). The south-
sightings were lower for 2007, 2008 and 2009. There were west had the highest density of sightings (0. 64 sightings km21),
no sightings data available for 2003, 2010 or 2011 higher than the north-east (0.22 sightings km21), the north-
(Figure 2A). Seasonality was clearly evident with the west (including Northern Ireland) (0.15 sightings km21)
number of records peaking in the months of June and July and the south-east, which presented the lowest (0.13
(Figure 2B). sightings km21); species richness was also greatest in the
The most commonly sighted species was R. octopus (N ¼ south-west (Figure 4A). The Bristol Channel had the highest
499, 52.5% (of validated records)) (Figure 2C). Five other incidence of species-specific cnidarian aggregations (Figure 4B).
species were regularly sighted: A. aurita (N ¼ 139, 14.6%); Of the most commonly sighted species, A. aurita were ubi-
C. capillata (N ¼ 95, 10%); C. hysoscella (N ¼ 86, 9%); C. quitously distributed (Figure 3B), C. capillata and C. hysoscella
lamarckii (N ¼ 100, 10.5%); and V. velella (N ¼ 32, 3.4%). had a clear north/south divide in their distributions (Figure
Of these, R. octopus and V. velella were sighted throughout 3C, D) and C. lamarckii had a greater number of sightings
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https://doi.org/10.1017/S00253154140001371404 stephen k. pikesley et al.
Fig. 2. Sightings for all cnidarian species expressed as a percentage of sightings from 2004 to 2009 (Harlech Bay database); (A) by year; (B) by month; (C)
species-specific sightings expressed as a percentage of all sightings from 2004 to 2009; (D) species-specific sightings by month. Box widths are proportional to
the square-roots of the number of observations in the box, outliers are not drawn. In (A) and (B) R. octopus sightings are shown as mid-grey, all other species
as black. In (C) and (D) species are identified as in Figure 1. The inset in part (C) shows the location of Harlech Bay in relation to the UK.
to the south-west and north-east (Figure 3E). The key areas (e.g. Doyle et al., 2007; Bastian et al., 2011a). Rhizostoma
for sightings of R. octopus were the coastal waters of Wales octopus had the longest sighting season of all Scyphozoa,
and western Scotland (Figure 3G). Pelagia noctiluca, P. physa- which may be attributable to this species surviving into
lis and V. velella were predominantly sighted to the south and winter at greater depths (Russell, 1970). The seasonality of
west of the UK (Figure 3F, H, I). R. octopus sightings also reflected previous studies (Doyle
et al., 2007).
Seasonality of Hydrozoa sightings varied considerably.
DISCUSSION Within the main database Velella velella were sighted March
to January whereas Physalia physalis were predominantly
Six species of scyphomedusae are indigenous to UK coastal sighted in late August, this was driven by mass sightings
waters (Russell, 1970). A typical scyphozoan life cycle results events in 2008 and 2009. Within the Harlech Bay data, sight-
in adult medusae being present in the water column during ings of V. velella were recorded throughout the year; no sight-
the summer months (Figure 5). The presence of adult ings were recorded for P. physalis. This lack of sightings for P.
medusae then characteristically decreases through the physalis seems contradictory, as both V. velella and P. physalis
autumn once eggs or planulae have been released. With the are oceanic, surface free-floating species, and therefore their
exception of the holopelagic Pelagia noctiluca, a suitable distribution has the potential to be driven by prevailing wind
shallow, shaded, benthic substrata is required for attachment conditions. Velella velella and P. physalis had similar spatial
of these planulae and further development of the scyphistoma distribution patterns, with the majority of sightings from
(Russell, 1970). Both the main sightings database and the south-west shores. However, closer inspection revealed that
Harlech Bay subset reflected this life cycle, with seasonality P. physalis tended to be concentrated to the south of this
of sightings of adult medusae clearly evident. The majority region and V. velella to the north. This fine-scale nuance in dis-
of Scyphozoa sightings occurred in the months of June, July tribution may be an artefact of P. physalis sightings being asso-
and August; Aurelia aurita and Cyanea lamarckii appeared ciated with the mass sightings events of 2008 and 2009.
earlier in the season than Cyanea capillata and Chrysaora There was no clear temporal trend in annual cnidarian
hysoscella, similar patterns have been previously recorded sightings within the main database or the Harlech Bay
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https://doi.org/10.1017/S0025315414000137cnidaria in uk coastal waters 1405
Fig. 3. Spatial distribution of sightings from 2003 to 2011 (main database), for (A) all species and (B –I) specified species, as detailed in figure parts.
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https://doi.org/10.1017/S00253154140001371406 stephen k. pikesley et al.
Table 1. Cnidaria sightings for UK coastal regions as defined in
Figure 4B.
UK region Total sightings Coastal Sightings
length (km) (km21)
North-east 763 3480 0.22
North-west (including 1387 9381 0.15
Northern Ireland)
South-east 453 3391 0.13
South-west 2376 3709 0.64
subset; however, sightings from Harlech Bay decreased
between 2007 and 2009. This decrease may be attributable
to a diminished survey effort, although preceding years repre-
sented near continuous survey effort (MCS, personal commu- Fig. 5. A typical Scyphozoa life cycle. A suitable shallow, shaded, benthic
nication). The main database showed inter-annual variability substrata is required for attachment of planulae and further development of
the scyphistoma. Note: Pelagia noctiluca is an oceanic species with direct
with notable peaks and troughs. There was no correlation development and has no benthic stage; C. hysoscella is a hermaphrodite
between these and promotional effort of the sightings (Russell, 1970).
scheme or NAO. Timing and periodicity of recruitment of
planulae to the seabed depends on a number of biotic and
abiotic factors, such as sexual maturation and reproductive 2007), dissolved oxygen concentrations (Condon et al.,
strategy of the medusa, water temperature and turbulence, 2001) and prey availability (Han & Uye, 2010). Inter-annual
and physical characteristics of the substratum (Lucas, 2001). variability may also be driven by hydroclimatic forcing such
Subsequent development of the scyphistoma (budding/ as wind stress, temperature or currents (Lynam et al., 2004)
strobilation), has been linked with factors such as tempera- or through transition in climate regimes (Brodeur et al.,
ture, salinity, light intensity and photoperiod (e.g. Purcell, 2008). There is also evidence for contrasting relationships
Fig. 4. (A) Species richness for Cnidaria sighted from 2003 to 2011 (main database) in UK coastal waters. Total number of individual species present summed by a
50 × 50 km sampling grid; (B) Cnidaria aggregations for UK coastal waters from 2003 to 2011 (main database). Species-specific sightings of 100 Cnidaria or more
were summed using the same sampling grid as in (A). (A) and (B) are displayed in accordance with their respective monochrome shaded legend. UK regional areas
are drawn in part (B): north-west (NW); north-east (NE); south-east (SE); and south-west (SW).
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https://doi.org/10.1017/S0025315414000137cnidaria in uk coastal waters 1407
between climate indices and Scyphozoa abundance that may large-scale (spatial and temporal) coverage that would other-
also be related to locally variable oceanographic parameters wise be logistically and financially unfeasible. We also suggest
(Lynam et al., 2005b, 2011; Attrill et al., 2007). As this study that they have the potential to contribute significantly to base-
holds records for multiple species over a wide spatial extent, lines, providing both seasonality and distribution data (par-
it is unlikely that one environmental or biological parameter ticularly when data are derived from survey schemes that
can explain variability in temporal trends. The observed pat- are ongoing), from which future changes in patterns or
terns are likely manifest from environmental forcing resulting trends may be identified. The likelihood of important insights
in a combination of environmental and biological drivers being more robustly elaborated would be greatly increased by
influencing species biology. the incorporation of focused, effort-corrected surveys at loca-
Species-specific inter-annual variability was also evident, tions along the UK coastline, including all nil returns, in at
and the records of no one cnidarian species displayed a least some locations across the geographical footprint of the
uniform temporal pattern. There was a significant decreasing project.
trend for C. hysoscella. However, our data spans a short time-
frame (9 years) and this trend may not be representative of
long-term trends. Indeed, evidence exists for worldwide oscil- ACKNOWLEDGEMENTS
lations in jellyfish populations of approximate 20 year period-
icity (Condon et al., 2013). However, robust detection of The authors thank Derryck Greenwood and all participants in
trends in jellyfish populations are hampered by a lack of a the Marine Conservation Society (MCS) jellyfish survey who
defined baseline; more specifically there is a paucity of long- generously contributed their data. The authors acknowledge
term data sets, .20 years (Condon et al., 2012). the constructive input from two anonymous referees and
The south-west region had the highest number of sightings the Associate Editor.
(and greatest coastline densities), greatest species richness,
and also had the highest incidence of cnidarian aggregations.
Aurelia aurita were universally distributed throughout the FINANCIAL SUPPORT
regions with highest abundance of all species, this is recog-
nized as a cosmopolitan species (Russell, 1970; Lucas, 2001). This work was funded by MCS. B.J.G. receives funding from
However, there were clear geographical demarcations the EU (Interreg 3a-MERiFIC; Intelligent Energy SOWFIA;
between some species; C. hysoscella were nearly always European Social Fund) and the Natural Environment
observed in southerly waters, whereas C. capillata were Research Council.
sighted in northerly waters. This spatial delineation probably
reflects the availability of suitable thermal niches for these
species (Holst, 2012). Rhizostoma octopus were principally Supplementary materials and methods
sighted in coastal waters of western Scotland and Wales. The supplementary material refered to in this paper can be
The Harlech Bay database identified this area as a hotspot found online at journals.cambridge.org/mbi.
for R. octopus, with this species accounting for 57% of all
sightings between 2004 and 2007, although there was a
marked decrease of sightings during 2008/2009, the reason
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